docs: def get_selector(self, name):
          """Find a selector mapped to a style in this or a base style sheet.
  
          Args:
              name (str): a style name
  
          Returns:
              :class:`.Selector`: the selector mapped to the style `name`
  
          Raises:
              KeyError: if the style `name` was not found in this or a base
                  style sheet
  
          """
  
          try:
              return self.matcher.by_name[name]
          except (AttributeError, KeyError):
              if self.base is not None:
                  return self.base.get_selector(name)
              else:
                  raise KeyError("No selector found for style '{}'".format(name))